Synthesis, characterization and evaluation of sonochemically generated materials.

摘要

The first chapter discusses the role of transition metal sulfides in hydrodesulfurization, and in part reviews electronic factors effecting activity of different sulfides, as well as the basis and nature of the promotional effect.; The second chapter deals with synthesis, characterization and sonochemically generated MoS₂-based catalysts. Co, Ni and Co-Ni Promoted/supported MoS₂ catalysts have been synthesized by sonochemical decomposition of metal carbonyls in presence of sulfur (and support, if applicable) in isodurene. Electron microscopy (SEM, TEM) shows that catalysts decorate the exterior surface of the alumina support, and that sonochemical catalysts have much higher dispersion and edge density than the commercial counterparts. Sonochemically generated catalysts have three to sevenfold higher activities for HDS of DBT, with identical selectivity towards biphenyl with comparable or better stability.; The third chapter discusses the nature and structure of the promoter atom in Co-promoted MoS₂ using XAS. Analysis of the Co K-edge data for the industrial catalyst suggests that Co neighbors 1–2 Mo atoms at a distance of 2.89 Å is coordinated to four or five sulfur atoms at a distance of 2.26 Å. The sonochemical catalyst is similar, with Co-S coordination of 5.0 ± 0.8 at a distance of 2.24 Å. The intensity of the Co 1s → 3d transition peak suggests that the Co in these catalysts is in a pseudo-centrosymmetric environment. We have concluded that Co has a distorted square planar or tetrahedral structure, which becomes square pyramidal upon the coordination of a substrate.; In the fourth chapter we have studied the effects of experimental parameters on size distribution of sonochemically generated Fe colloids. It has been found that changing temperature, precursor concentration, stabilizer amount, frequency, and sparging gas has no noticeable effect on the size distribution of Fe colloids, which remain in the 3–12 nm range. We have concluded that the size distribution does not change significantly because small Fe particles (∼0.4 nm with MP ≈ 350 K) melt together and coalesce to form larger (3–12 nm) particles, at which point the melting temperature is high enough that makes further coalescence unlikely.